Sphingomyelins are the major phospholipid components of biological membranes and plasma lipoproteins. Sphingomyelins consist of a ceramide core (sphingosine bound to a fatty acid via an amide linkage) and a phosphorylcholine head group (Formulae I, left). Dihydrosphingomyelins are the saturated homologues of sphingomyelins, and have a saturated ceramide core, namely dihydrosphingosine bound to a fatty acid via an amide linkage (Formulae I, right).

The sphingosine typically found in naturally occurring sphingomyelin is D-erythro-sphingosine an 18-carbon amino alcohol with an unsaturated hydrocarbon chain having a stereo chemical configuration of D-erythro. The IUPAC name for this sphingosine is (2S,3R,E)-2-aminooctadec-4-ene-1,3-diol (Compound A). The dihydrosphingosine, D-erythro-dihydrosphingosine, is its saturated homologue with the IUPAC name (2S,3R)-2-aminooctadecane-1,3-diol (Compound B).
Commercially available sphingomyelins are usually naturally products that comprise mixtures of naturally occurring sphingomyelins. The actual composition of this mixture varies depending on the biological source and contains various fatty acid chain lengths. The N-palmitoyl-sphingomyelin is a major component in the natural sphingomyelins.
N-Palmitoyl-D-erythro-sphingomyelin (Compound C), one of the isomers of palmitoyl sphingomyelin, which has the IUPAC name N-((2S,3R,E)-1,3-dihydroxyoctadec-4-en-2-yl)palmitamide, is believed to be the main naturally-occurring isomer. Its corresponding dihydrosphingomyelin, N-palmitoyl-D-erythro-dihydrosphingomyelin (Compound D), has the IUPAC name (2S,3R)-3-hydroxy-2-palmitamidooctadecyl(2-(trimethylammonio)ethyl)phosphate.

Industrially and economically-relevant synthetic alternatives of this natural source of sphingomyelin have yet to be developed. Synthetic pathways known in the art have not been useful for the large scale synthesis of sphingomyelins, particularly those with fatty acids having 12 to 25 carbons.
The ceramides N-palmitoyl-D-erythro-sphingosine (Compound E) and N-palmitoyl-D-erythro-dihydrosphingosine (Compound F) are intermediates in the synthesis of N-palmitoyl-D-erythro-sphingomyelin and N-palmitoyl-D-erythro-dihydrosphingomyelin, respectively.
